1. Field of the Invention
The present invention relates to the preparation of silane, and, more especially, to the preparation of silane by the hydrogenation of chlorosilanes in a bath of molten salts.
2. Description of the Prior Art
The preparation of silane, SiH.sub.4, by reacting chlorosilanes, SiH.sub.4-x Cl.sub.x, with lithium hydride is known to this art. This reaction can be carried out in a bath of molten salts, consisting, in particular, of a eutectic mixture of lithium chloride and potassium chloride, which melts at about 360.degree. C. The reaction can be represented as follows: EQU 4LiH+SiCl.sub.4 .fwdarw.SiH.sub.4 +4LiCl.
The silane (SiH.sub.4) produced is gaseous and it is removed continuously. The lithium chloride thus formed enriches the bath, and such bath can be diverted to a zone of electrolysis zone into which hydrogen is introduced to re-form lithium hydride such that the aforesaid reaction scheme can continue to proceed.
Practically, however, the noted process has a significant disadvantage.
Indeed, the reaction of chlorosilanes with lithium hydride is highly exothermic, with the result that the silane formed partially decomposes in the bath of molten salts, according to the reaction: EQU SiH.sub.4 .fwdarw.Si+2H.sub.2
This reaction becomes substantial at about 400.degree.-450.degree. C.
Consequently, the yields of SiH.sub.4 are never quantitative and range from 40 to 80% at most.